Kim Jong-Un spoke of “a new history of peace, prosperity and inter-Korean relations” as he became the first North Korean leader to step across the border into South Korea since the end of the Korean war in 1953.

Kim was meeting South Korean President Moon Jae-In after a sudden thaw in relations between the two nations on the Korean peninsula.

The two leaders met in the heavily fortified demilitarized zone to talk about the prospects for peace and reconciliation, and specifically, the denuclearization of the peninsula.

The handshake between the two men in no way seals a peace deal. But it may start a process that brings the two Koreas much closer together. There are some huge challenges to overcome if the two nations are to move in a direction that could create the conditions for North and South to integrate more closely, or ultimately, re-unify.

One question is how much the South might be willing to contribute to the vast cost of transforming North Korea’s dilapidated economy into something fit for the globalized 21st century.

The image above shows the two Korean nations at night, and illustrates how far the North has fallen behind the South in terms of energy supply infrastructure and generation capacity.

It is hard to gauge the concerns of those in the North, but to people in the South, worries about how closer ties might affect their economy could become crucial.

According to an annual report by Seoul National University, South Korean support for re-unification has fallen. Last year, 53.8% said they viewed unification as “necessary,” compared with more than 63% in 2007, Reuters reported.

“South Korea now stands shoulder to shoulder with advanced countries after having climbed up from being one of the poorest countries in the world, thanks to the blood and sweat of our parents’ generation,” a 35-year-old office worker in Seoul told Reuters. “After unification, everything will go back to as it was when we were a developing country.”

The North, land-linked to China, has been led by a family line of autocratic rulers who have limited access to the outside world. International sanctions and internal government policy have combined to keep most of the republic’s population in poverty.

Meanwhile, the South, bordered by the Sea of Japan, has developed a vibrant democracy based on modern industries and finance that has led to it becoming the fourth-largest economy in the region based on its 2016 gross domestic product.

Following the war in the 1950s, the US, Japan and their allies helped to rebuild South Korea. The North turned to Russia, China and the nations in the Communist sphere of influence, which between them supplied almost 880 million roubles as well as manpower and technological input.

The result, according to historian Charles K Armstrong, was that: “In the late 1950s, North Korea’s growth rate of total industrial output (averaging 39% between 1953 and 1960) was probably the highest in the world.”

However, in the decades since, the South has become a powerhouse of innovative industries, including microchip technologies and the automotive sector, generating a GDP of more than $1.4 trillion in 2014.

The economy of the North, however, is still dependent on sales of coal to China, while sanctions have limited its ability to trade and access the global finance system. After China, its biggest trade partners are India and Russia and its 2014 GDP, said to be its highest ever, was $17.4 billion.

Degrees of separation

The South is a modern place with a strong and internationally popular music scene, and where high-tech lifestyles abound. It has a respected system of universal healthcare and an average life expectancy of about 80.

North Korea, by comparison, has a low penetration of mobile devices, suffers frequent harvest failures, requires regular international aid to feed its people and has an average life expectancy of just over 70.

Marrying up the reconstruction needs of the North while growing the economy of the South might be a tricky path to negotiate for any government minded to re-unify the two.

Another worry for South Koreans is what role Kim Jong-Un would have to play in any future unified state.

While the historic meeting of the two leaders is unlikely to address this last issue, the fact that it happened at all shows a rapprochement between the sides that would have seemed unimaginable even a few months ago.